1. Field of the Invention
The present invention relates generally to integrated circuits, and more particularly, to monitoring circuit performance variations that may arise from variations in any one or more of manufacturing process, temperature or voltage.
2. Description of the Related Art
Variations in process, temperature and voltage (PVT) can influence the performance of an integrated circuit. For example, fluctuations in semiconductor manufacturing processes can result in variations in gate oxide thickness and doping concentrations, which can change transistor threshold voltage. Moreover, the mobility of charge carriers and the threshold voltage may vary with temperature. Thus, there has been a need to monitor and compensate for PVT induced variations in integrated circuit performance.
There are many prior approaches to monitoring and compensating for PVT variations. For instance, ring oscillators have been used to measure the number of ring oscillator cycles during a number of reference clock cycles. A ring oscillator may serve as a useful reference circuit since PVT variations ordinarily will influence its oscillation frequency. PVT induced changes in the ring oscillator frequency typically are indicative of PVT induced changes in the performance of other circuit components located on the same semiconductor chip. Also, some other prior approaches to PVT monitoring involved analogue measurement techniques.
While these past techniques for monitoring and compensating for PVT related variations in circuit performance generally have been acceptable, there has been a need for improvement. For example, there has been a need for a compact monitoring circuit that can provide an improved indication of the impact of PVT variations upon circuit performance over a wide range of reference frequencies, on an measurement scale that is independent of reference frequency. The present invention meets this need.